Knowing how to write grammatically correct sentences is an ability that can help you in all facets of life. In business writing, media writing or even in writing personal letters and emails, proper grammar helps you portray your message clearly and projects intelligence on your part. By following a few simple rules, you can learn how to use the comma and semicolon correctly.
Use a comma to separate two independent clauses joined by a conjunction. Independent clauses are those that can stand alone as sentences if they had to -- meaning they contain at least a subject and a verb. The Purdue University Online Writing Lab offers this example: "I am going home, and I intend to stay there."
Insert commas between lists of three or more. For example: "She will split the money between her sister, brother and daughter." Some grammarians choose to add a second comma before the word "and" in sentences such as this one, but using that comma has become a matter of preference rather than an hard-and-fast rule.
Use commas when an "ly" adjective is used with other adjectives. "The Blue Book of Punctuation and Grammar" gives this example: "Felix was a lonely, confused boy." Be careful here not to confuse "ly" adverbs with adjectives as "ly" adverbs don't necessarily need commas after them.
Use a comma inside quotation marks at the conclusion of a quote if you are adding attribution at the end. For example: "She likes to run and play," he said.
Use a semicolon between two closely related independent clauses. Grammar Girl gives this example: "I have a big test tomorrow; I can't go out tonight."
Place semicolons in sentences with complex lists. Grammar Girl gives this example: "This week's winners are Joe from Reno, Nevada; Diane from Phoenix, Arizona; and Matt from Irvine, California."
Use a semicolon to create variety in your sentences, especially if you have a lot of choppy sentences in a row. Place a coordinating conjunction between the two sentences you bring together with the semicolon. Here's another example from Grammar Girl: "If you want me to go out tonight, you need to help me with my homework first; and if you say no, I'll know that you don't really care about going out."